Venomous Critters of the Southwestern Deserts


Venomous Critters of the Southwestern Deserts

By Jeff DeBellis

Illustrations by T.B.R. Walsh

“Those who travel in desert places do indeed meet with creatures surpassing all description.”

–Cormac McCarthy, Blood Meridian

Deserts are generally inhospitable places. They’re either too hot, too cold, too dry, or too windy. Sandstorms, monsoons, and flash floods ravage the land. The plants are spiky and the animals are venomous. Nonetheless, people like to visit the desert. A lot of people. Because despite the downsides, deserts are beautiful.

There are three distinct hot deserts in the American Southwest – the Chihuahuan, the Sonoran, and the Mojave. The Chihuahuan Desert covers southern New Mexico, western Texas, the extreme southeastern corner of Arizona, and extends into the Mexican states of Chihuahua, Coahuila, and Durango. The Sonoran Desert extends from southern Arizona and southeastern California into the Mexican state of Sonora. The Mojave covers southeastern California, southern Nevada, northwestern Arizona, and a tiny corner of southwestern Utah. The boundaries of the three deserts are determined by the distribution of plant and animal species. In some cases, the individual deserts are bounded by mountain ranges that form “sky islands” of more temperate habitat. Hot deserts differ from cold deserts (like the Great Basin farther north) in that most of their precipitation comes in the form of rain, as opposed to snow.

Deserts are home to a startlingly wide variety of plants and animals that have adapted to the harsh conditions. The Chihuahuan Desert is one of the most biodiverse arid regions on Earth. Most desert animals are not actually venomous. Regardless, all wild animals should be appreciated only from a safe distance. The creatures that are venomous include reptiles, such as snakes and Gila monsters, and arachnids, including spiders, scorpions, and to a lesser degree, tarantulas. This article describes many of the venomous species that are native to the region.



Rattlesnakes live nearly everywhere in the United States, but they are especially abundant in the southwest. There are 36 species in the western hemisphere, 17 in the U.S., and 14 in the southwestern deserts. The most poisonous of these are the Mojave rattlesnake (Crotalus scutulatus), with an LD50 SC of 0.31 mg/kg, and the tiger rattlesnake (Crotalus tigris), with an LD50 SC of 0.21 mg/kg. The LD50, also known as the median lethal dose, indicates how much venom it takes for a snake to kill 50% of its prey. The lower the number, the more potent the venom. The “SC” refers to subcutaneous injection, which is the most common way that humans are exposed to the venom. For comparison, the timber rattlesnake of the Eastern United States has an LD50 SC of 2.25 mg/kg.

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By Frank Hubbell, D.O.


It is impossible to accurately count the number of venomous snakebites worldwide, simply because most occur in rural and remote areas where access to medical care is limited, statistics are not kept, and snakebites are not reported.


There are reportedly 421,000 envenomations per year with 20,000 deaths.

But, snakebites and deaths from snakebites are grossly underreported.

It is estimated that the real numbers could be as high as 1,841,000 envenomations with 94,000 deaths per year.

 United States:

Approximately 8000 venomous snakebites are reported each year with 5 – 10 deaths per year.




       carnivorous reptiles

       lack eyelids

       lack external ears

       ectothermic (cold-blooded)

       most are amniote vertebrates (lay eggs that contain amniotic fluid, suitable for the terrestrial environment), some snakes do have live births

       covered in overlapping scales

       most kill by swallowing their prey whole or death by constriction

       of the 3,400 species, 300 are venomous and use their venom to kill, subdue, and digest their prey


Kingdom – Animalia

Phylum – Chordata

Class – Reptilia

Order – Squamata

Suborder – Serpentes

Family – 20 different families

4 families are venomous

Genera – 500 different Genera

Species – 3,400 different species

3,100 are nonvenomous

300 are venomous


Interestingly enough, venomous snakes can be divided into different families based on their dentition and types of fangs, not as you might suspect, by the type of venom they possess. The rest of snakes are fangless, aglyphous.

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